题解 | #密码截取#

s = input()
# 奇数类型：ABA
# 偶数类型：ABBA
max_len = 1
# 奇数
for i in range(len(s)):
    left, right = i, i
    while left >= 0 and right < len(s) and s[left] == s[right]:
        if max_len < right - left + 1:
            max_len = right - left + 1
        left -= 1
        right += 1
# 偶数
for i in range(len(s)):
    left, right = i, i + 1
    while left >= 0 and right < len(s) and s[left] == s[right]:
        if max_len < right - left + 1:
            max_len = right - left + 1
        left -= 1
        right += 1
print(max_len)